FERRO-MANGANESE AND SPIEGELEISEN 197 As impurities, ferro-silicon contains small quantities of carbon, manganese, phosphorus, sulphur and, sometimes, calcium. Phosphorus is an injurious con- stituent, the maximum allowable limit being 0-15-0-2%. The mean percentage compositions of the commoner commercial forms are (Geiger) : TABLE XV Compositions of Ferro-silicons I II m IV V VI Silicon .... 25-89 29-66 5I-80 53-75 51-20 75-67 Iron ..... 72-92 72-99 47-30 45-09 48-89 23-01 Carbon ..... 0-5^ O'^O Manganese 0-42 0-56 o-35 o-ii o-37 0-26 Sulphur .... 0-03 o-oi 0-O2 0-005 0-007 o-oi Phosphorus 0-04 0-30 O-O4 0-041 0-04 0-04 Aluminium 0-30 0-60 0-17 Chromium. 0-25 ----- Copper ..... ----- 0-04 Lime ..... " ----- 0-05 O-2I FERRO-MANGANESE AND SPIEGELEISEN Ferro-manganese is usually obtained in the blast furnace from a mixture of iron and manganese minerals, and serves for the de-oxidation of steels and for the preparation of manganese steels and other special alloys. It is slightly yellowish white, compact and with a granular structure inter- sected, especially in the high percentage types, by bluish, iridescent, acicular crystals. Spiegeleisen is a form of white cast-iron very rich in manganese with a peculiar lamellar structure and a sliining and sometimes iridescent surface ; it has the same uses as ferro-manganese. Analysis of these products may include, besides the determination of the manganese, also those of the carbon, silicon, phosphorus, sulphur, etc., which are always present in the commercial products in larger or smaller quantities. 1. Determination of the Manganese.Numerous methods, gravi- metric, volumetric and electrolytic, have been proposed for the determina- tion of the manganese in ferro-manganese and manganiferous cast-irons in general. The following will be described : Volhard's volumetric method with the recent modifications introduced by Wolff, Schb'ffel and Donath, and the electrolytic method. (a} VOLUMETRIC DETERMINATION. This method is based on the fact that, if a neutral solution of a manganese salt is treated with potassium per- manganate, the whole of the manganese in it is oxidised at the expense of the permanganate and precipitated, together with that contained in the added permanganate, as the dioxide. The manganese present is calculated from the amount of permanganate necessary for the oxidation.olybdate reagent.